Immunoregulatory capacity of mesenchymal stem cells (MSC) is triggered by the inflammatory environment, which changes during tissue repair. Macrophages are essential in mediating the inflammatory response after injury and can adopt a range of functional phenotypes, exhibiting pro-inflammatory and anti-inflammatory activities. An accurate characterization of MSC activation by the inflammatory milieu is needed for improving the efficacy of regenerative therapies. In this work, we investigated the immunomodulatory functions of MSC primed with factors secreted from macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype. We focused on the role of TNF-α and IL-10, prototypic pro-inflammatory and anti-inflammatory cytokines, respectively, as priming factors for MSC. Secretion of immunoregulatory mediators from human MSC primed with media conditioned by human macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype was determined. Immunomodulatory potential of primed MSC on polarized macrophages was studied using indirect co-cultures. Involvement of TNF-α and IL-10 in priming MSC and of PGE2 in MSC-mediated immunomodulation was investigated employing neutralizing antibodies. Collagen hydrogels were used to study MSC and macrophages interactions in a more physiological environment. Priming MSC with media conditioned by pro-inflammatory or anti-inflammatory macrophages enhanced their immunomodulatory potential through increased PGE2 secretion. We identified the pro-inflammatory cytokine TNF-α as a priming factor for MSC. Notably, the anti-inflammatory IL-10, mainly produced by pro-resolving macrophages, potentiated the priming effect of TNF-α. Collagen hydrogels acted as instructive microenvironments for MSC and macrophages functions and their crosstalk. Culturing macrophages on hydrogels stimulated anti-inflammatory versus pro-inflammatory cytokine secretion. Encapsulation of MSC within hydrogels increased PGE2 secretion and potentiated immunomodulation on macrophages, attenuating macrophage pro-inflammatory state and sustaining anti-inflammatory activation. Priming with inflammatory factors conferred to MSC loaded in hydrogels greater immunomodulatory potential, promoting anti-inflammatory activity of macrophages. Factors secreted by pro-inflammatory and anti-inflammatory macrophages activated the immunomodulatory potential of MSC. This was partially attributed to the priming effect of TNF-α and IL-10. Immunoregulatory functions of primed MSC were enhanced after encapsulation in hydrogels. These findings may provide insight into novel strategies to enhance MSC immunoregulatory potency.

Background: The mechanisms by which macrophage phenotype contributes to mesenchymal stem cells (MSC)-mediated bone repair remain unclear. In this work, we investigated the influence of factors released by human macrophages polarized to a pro-inflammatory or an anti-inflammatory phenotype on the ability of human MSC to attach, migrate, and differentiate toward the osteoblastic lineage. We focused on the role of TNF-α and IL-10, key pro-inflammatory and anti-inflammatory cytokines, respectively, in regulating MSC functions.Methods: MSC were treated with media conditioned by pro-inflammatory or anti-inflammatory macrophages to study their influence in cell attachment, migration, and osteogenic differentiation. The involvement of TNF-α and IL-10 in the regulation of MSC functions was investigated using neutralizing antibodies and recombinant cytokines.Results: Treatment of MSC with media conditioned by pro-inflammatory or anti-inflammatory macrophages promoted cell elongation and enhanced MSC ability to attach and migrate. These effects were more noticeable when MSC were treated with media from pro-inflammatory macrophages. Interestingly, MSC osteogenic activity was enhanced by factors released by anti-inflammatory macrophages, but not by pro-inflammatory macrophages. Significant IL-10 levels originated from anti-inflammatory macrophages enhanced MSC osteogenesis by increasing ALP activity and mineralization in MSC layers cultured under osteogenic conditions. Moreover, macrophage-derived IL-10 regulated the expression of the osteogenic markersRUNX2,COL1A1, andALPL. Notably, low TNF-α levels secreted by anti-inflammatory macrophages increased ALP activity in differentiating MSC whereas high TNF-α levels produced by pro-inflammatory macrophages had no effects on osteogenesis. Experiments in which MSC were treated with cytokines revealed that IL-10 was more effective in promoting matrix maturation and mineralization than TNF-α.Conclusions: Factors secreted by pro-inflammatory macrophages substantially increased MSC attachment and migration whereas those released by anti-inflammatory macrophages enhanced MSC osteogenic activity as well as cell migration. IL-10 was identified as an important cytokine secreted by anti-inflammatory macrophages that potentiates MSC osteogenesis. Our findings provide novel insights into how environments provided by macrophages regulate MSC osteogenesis, which may be helpful to develop strategies to enhance bone regeneration.

Ultra-high-molecular-weight polyethylene sterilised in the absence of air and highly cross-linked polyethylene have been used to avoid osteolysis and loosening in total hip replacement. Our prospective randomised study has assessed the results using two different polyethylenes associated with the same prosthetic design. We assessed 45 Allofit acetabular components with a Sulene-polyethylene liner of conventional polyethylene gamma sterilised with nitrogen and 45 Allofit acetabular components with a Durasul-polyethylene liner sterilised in ethylene oxide, both matched with an Alloclassic stem with a 28 mm modular femoral head. The prostheses were implanted between May 1999 and December 2001. The mean follow-up was for 66.3 months (60 to 92). The linear penetration of the femoral head was estimated at 6 weeks, at 6 and 12 months and annually thereafter from standardised digitised radiographs using image-analysis software.There was no loosening of any prosthetic component. There were no radiolucent lines or osteolysis. The mean rate of penetration calculated from regression analysis during the first five years was 38 μm/year (sd 2) for the Sulene group and 6 μm/year (sd 1) for the Durasul group (p = 0.00002). The rate of penetration of the Durasul group was 15.7% of that of the Sulene group.

Between 1999 and 2001, 90 patients underwent total hip replacement using the same uncemented acetabular and femoral components with a 28 mm metallic femoral head but with prospective randomisation of the acetabular liner to either Durasul highly cross-linked polyethylene or nitrogen-sterilised Sulene polyethylene. We assessed 83 patients at a minimum follow-up of ten years. Linear penetration of the femoral head was estimated at six weeks, six and 12 months and annually thereafter, using the Dorr method, given the non-spherical shape of the acetabular component. There was no loosening of any component; only one hip in the Sulene group showed proximal femoral osteolysis. The mean penetration of the femoral head at six weeks was 0.08 mm (0.02 to 0.15) for the Durasul group and 0.16 mm (0.05 to 0.28) for the Sulene group (p = 0.001). The mean yearly linear penetration was 64.8% lower for the Durasul group at 0.05 mm/year (sd 0.035) for the Sulene group and 0.02 mm/year (sd 0.016) for the Durasul (p < 0.001). Mean linear femoral head penetration at ten years was 61% less in the Durasul than Sulene group. Highly cross-linked polyethylene gives excellent results at ten years. Cite this article: Bone Joint J 2013;95-B:326–32.

Most acetabular revisions are managed with cementless hemispherical or elliptical metal implants relying on bone ingrowth. Nonetheless, loss of acetabular bone stock and inability to achieve secure component fixation represent challenges in the setting of revision total hip arthroplasty. Impaction bone grafting (IBG) using allograft represents one option for treatment of this problem. However, cup migration and bone graft resorption are limitations when IBG is used for large segmental defects, and the precise role of IBG as well as the use of mesh (and the kinds of defects for which mesh does not work well) in this setting remains unknown.

Uncemented press-fit cups provide bone fixation in primary THA, but the use of screws is sometimes necessary to achieve primary stability of the socket. However, it is unclear whether and when screws should be used. We analyzed the factors related to screw use with a press-fit uncemented cup and assessed whether screw use is associated with the same rates of loosening and revision as a press-fit technique. We retrospectively reviewed 248 patients who underwent THA using the same prosthetic design. Eighty-eight hips had screws to achieve primary cup fixation (Group 1), and 189 did not (Group 2). Mean age was 50 years (range, 14–73 years). We analyzed factors related to the patient, acetabular type, and reconstruction of the rotation center of the hip. Minimum followup was 5 years (mean, 8.9 years; range, 5–12 years). We found higher screw use in women, patients with less physical activity, Acetabular Types A or C, and a distance from the center of the prosthetic femoral head to the normal center of rotation of more than 3 mm. There were four revisions in Group 1 and five in Group 2. Eight hips had radiographic loosening in Group 1 and nine in Group 2. Cups with a postoperative abduction angle of more than 50° had a higher risk for loosening. Press fit was achieved less frequently in women and patients with Acetabular Types A or C and less physical activity; a closer distance to the normal center of rotation decreased screw use. Screw use to augment fixation achieved survival similar to that of a press-fit cup. Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence